The manufacture of printed circuit boards has experienced considerable improvement over recent years: Technological advancements in chemistry, machinery, and materials have resulted in the ability to consistently produce large volumes of printed circuit boards with dense circuitry patterns on a highly efficient basis. One particular area of progress has been in the drilling process associated with printed circuit boards. An individual circuit board typically includes thousands of small-diameter drilled holes which are used to connect various components to the board by accommodating the leads or pins thereof, to connect the circuitry traces of one layer to another, to provide reference points for subsequent processing, and to assist in mounting the complete circuit board within its final housing. In one currently known circuit board manufacturing process, a plurality of circuit boards are drilled simultaneously by maintaining the circuit boards in a contiguous, overlapped orientation. In another currently known fabrication technique, several circuit boards are placed on a panel for processing, with a single panel typically including tens of thousands of drilled holes.
As will be recognized, due to the extremely small diameter of the holes typically drilled in the printed circuit boards, the associated drill bits are formed having small diameter cutting tips and are made of an extremely hard, wear resistant material such as tungsten carbide. Though this material is resistant to wear, after a certain number of drilled holes ("hits"), the drill bit will typically deteriorate and will no longer be sharp enough to maintain the diameter and tolerance requirements for subsequent holes. Through experience, circuit board manufactures have approximated the rate at which drill bits dull. Based upon this wear rate, the drill bit is typically replaced after a certain number of hits.
During the printed circuit board manufacturing process, the depth to which the cutting tip of the drill bit penetrates, i.e., extends into, the circuit board(s) must also be tightly controlled. In this respect, the drill bits used to facilitate the drilling operation are typically provided with a locating ring disposed about the shank portion thereof which serves as a stop for accurately locating the drill bit, the collet, or the tool holder of the rotary drilling apparatus. Due to the importance of tightly controlling the penetration depth of the cutting tip of the drill bit into the circuit board(s), the distance separating the cutting tip from the-locating ring must itself be tightly controlled, thus necessitating the precise positioning of the locating ring upon the shank portion of the drill bit.
In view of the difficulty and expense associated with the manufacture of carbide drill bits with small diameter cutting tips, once the cutting tip of the drill bit becomes dull, the same is typically re-sharpened rather than being discarded. As will be recognized, due to the importance of drilling all the holes within the circuit board(s) within closely held tolerances, the re-sharpening of the cutting tip of the drill bit must be accomplished in a precise, highly accurate manner. Additionally, since the re-sharpening procedure often results in a slight loss of length from the cutting tip region of the drill bit, the distance separating the cutting tip from the locating ring must be maintained within a certain, tightly controlled range. In this respect, the shortening of the drill bit which occurs as a result of the re-sharpening procedure requires that the position of the locating ring upon the shank portion be adjusted so as to once again achieve the desired separation distance between the locating ring and the sharpened cutting tip.
The re-positioning of the locating ring upon the shank portion of the drill bit is typically accomplished manually through the utilization of conventional measurement techniques and devices such as calipers. Additionally, the re-sharpening of the cutting tip of the drill bit and subsequent measurement thereof to ensure compliance with tolerance requirements are often accomplished manually. However, as will be recognized, such manual re-positioning and re-sharpening techniques are extremely time consuming and thus expensive, and oftentimes do not accomplish the positioning of the locating ring relative the cutting tip and/or the re-sharpening of the cutting tip with the degree of accuracy needed to ensure that the subsequent drilling operation will be properly conducted.
There has yet to be developed in the prior art an completely automated system for accomplishing the verification of identity and differing geometries of various drill bits and the re-sharpening and re-positioning functions described above. One of the difficulties in automating the re-sharpening process is that the size and condition of the cutting tip of the drill bit often varies. In this respect, the cutting tip may be dirty, worn, undersize in diameter and/or length, chipped, or broken. Additionally, drill bits are typically sent for re-sharpening in large quantities, with such quantities including drill bits that are from different manufacturers, have different dates of original manufacture, are of differing styles and/or series, or are being subjected to a first or subsequent re-sharpening procedure.
The present invention specifically addresses the above-described deficiencies and obstacles by providing a completely automated system which automatically verifies the identity and geometry of drill bits, re-sharpens the cutting tip of a drill bit to within closely held tolerances, and accurately adjusts the positioning of the locating ring upon the drill bit subsequent to the re-sharpening of the cutting tip thereof.